number_of_loops no longer modifies input image, additional test case …

…for test_number_of_loops

feature_extraction.py

@@ -121,6 +121,8 @@ def number_of_loops(image: ndarray) -> int:
 
     assert isinstance(image, ndarray)
 
+    image = np.copy(image)
+
     BLACK, WHITE = 0, 1
     NUM_ROWS, NUM_COLS = len(image), len(image[0])
 

test_feature_extraction.py

@@ -230,8 +230,11 @@ def test_number_of_loops(self):
 
         # test custom expected values
         for digit, image in enumerate(self._images):
+            img_copy = image.copy()
             self.assertEqual(number_of_loops(image),
                              self._number_of_loops[digit])
+            self.assertTrue(np.array_equal(image, img_copy),
+                            'expected immutable image')
 
     def test_horizontally_split_symmetry(self):
         '''Tests the horizontally_split_symmetry function'''
@@ -348,5 +351,6 @@ def test_vertically_split_symmetry(self):
     def test_get_image_features(self):
         '''Tests the get_image_features function'''
 
+
 if __name__ == '__main__':
     unittest.main()